1. Field of the Invention
The present invention relates to a method for forming a contact plug. Especially, the present invention is utilized for fabricating a contact plug in VLSI (very large scale integrated circuit) such as MOS or bipolar devices (e.g., DRAM, SRAM, E.sup.2 PROM or mask ROM), CCD or the like.
2. Prior Art
Recently, LSI has been remarkably miniaturized, which has led to a highly reduced diameter of a contact hole. Conventional sputtering techniques for metal deposition cannot be used for plugging up the contact hole having subhalf micron diameter because of their poor step coverage. Instead of the sputtering techniques, there has been developed a selective tungsten deposition technique in accordance with CVD method.
A conventional method for forming a contact plug comprises, as shown in FIG. 2, depositing successively a silicate glass layer 12 and boron phosphorus silicate glass layer 13 on a semiconductor substrate 11 provided with a base device, fluidizing the boron phosphorus silicate glass layer by heating to planarize the surface thereof in order to complete a stacked interlayer insulator for a multilevel connection, forming a contact hole by photolithography at an intended contact region of the interlayer insulator, and then forming a contact plug 14 in the contact hole by the selective tungsten deposition in accordance with CVD method.
However, this method has a problem that the contact plug made of tungsten peels off at the interface.
The present invention is accomplished in order to solve the aforesaid problem and provides a method for forming a contact plug possessing excellent reliability without causing the peeling of the contact plug.